Minecraft Turtle: Spiral stairs

--[[
2016 (c) psychedelixx
Minecraft Spiralstairs (robust)
2016-10-14

Mines a 3x3 spiral stairs (downwards)

Robust API:
http://computercraft.info/wiki/Robust_Turtle_API

Usage:
    - use turtle and type "label set <name>"
      (to give your turtle an unique name so it remembers its programs)
    - type "pastebin get hYABpV27 spiralstairs"
    - type "spiralstairs <removeCenter 0|1>"
- place chests in slot 15
- place torches in slot 16
]]

chestSlot = 15
torchSlot = 16
centerRemoved = false

function placeChestIfFull()
    empty = 0
    for slot = 1, 14 do
        if turtle.getItemCount(slot) == 0 then
            empty = 1
            break
        end
    end

    --[[ if turtle is full, turn around, place chest, move items into it, turn around and continue ]]--
    if empty == 0 then
        t.up()
        t.turnAround()
        t.dig()

        if turtle.getItemCount(chestSlot) == 0 then
            print("Please put chests in slot 15 and press enter to continue")
            read()
        end

        turtle.select(chestSlot)
        turtle.place()

        for slot = 1, 14 do
            turtle.select(slot)
            turtle.drop()
        end

        t.turnAround()
        t.down()
    end
end

local args = { ... }

if #args ~= 1 then
    print("Usage: spiralstairs <removeCenter 0|1>")
    print("place chests in slot 15")
    print("place torches in slot 16")
    error()
end

if tonumber(args[1]) == 1 then
    removeCenter = true
else
    removeCenter = false
end

function removeCenterIfNeeded(x)

    if x%2 == 1 and removeCenter and not centerRemoved then
        t.left()
        t.dig()
        t.right()

        centerRemoved = true
    end
end

function placeTorchIfNeeded(x)

    if (x+1)%14 == 0 and turtle.getItemCount(torchSlot) > 0 then
        oldSlot = turtle.getSelectedSlot()

        t.right()
        t.place(torchSlot)
        t.left()

        turtle.select(oldSlot)
    end
end

print("======== 2016 (c) psychedelixx ========")
print("Let's go!")
print("Mining spiral stairs...")

if turtle.getItemCount(chestSlot) == 0 then
    print("")
    print("Warning: no chests found in slot 15. Press enter to continue")
    read()
end

if turtle.getItemCount(torchSlot) == 0 then
    print("")
    print("Warning: no torches found in slot 16. Press enter to continue")
    read()
end

x = 0
done = false

t.digDown()
t.down()

repeat
    t.dig()
    placeChestIfFull()
    t.forward()
    x = x + 1

    removeCenterIfNeeded(x)

    placeTorchIfNeeded(x)

    if x%2 == 0 then
        t.left()
    end

    if x%7 == 0 then
        turtle.place()

        if turtle.detectDown() then
            if t.digDown() then
                placeChestIfFull()
            end
        end
        if not t.down() then
            done = true
        end

        centerRemoved = false
    end
until done